Final Presentation Draft Slides

1. Final Presentation Draft Slides Description: Some draft slides and ideas 3/26/09 Kris Ezra Attitude 1

2. Areas of Analysis (Review) • Attitude Determination in Low Earth Orbit • Sun Sensors and Star Sensor are selected • Gimbaled Main Engine Alternative • Found that the propellant cost is higher for desaturation using main engines • Momentum Transfer Landing Alternative • Discarded since the required accelerations exceeded the limit of communications equipment • Spinning Tether Landing Alternative • Discarded due to large tether length and high mass cost • Arbitrary Payload Main Engine Selection • Recommended BHT-8000 for having lowest cost per kg • This is not currently in the report Kris Ezra Attitude

3. Attitude Determination in LEO Valley Forge Sun Sensors • Performance Accuracy:   +1 Degree • Mass: ~0.35 kg • Power Consumption :  2.5 Watts Peak • Operating Temperature: ~ -20 to +60 deg. C • Valley Forge Star Sensors • Performance Accuracy:   15 arcseconds • Mass:  <3.2 Kg • Dimension: 32 x 32 x 16 (cm) • Power Consumption : 10.2 W • Operating Temperature: -40 to +60 deg. C Total Attitude Determination Mass (Including Star Sensor): ~3.55 kg Package Cost (including attitude control equipment): $400,000 These numbers need updated. Specifically total attitude determination mass and dimensions of the sun sensor Kris Ezra Attitude

4. Gimbaled Main Engine Alternative 0.3858 m GimbalMount Specifications: • Approximate mass of 6 kg • Angular maximum motion of 20º • 3 Axis Gimbal 1.06 m 20º Show Formulation? Gimbal Alternative Discarded based on Mass Cost Kris Ezra Attitude Group Translunar Phase

5. Rationale for Discarding Momentum Transfer Concept: The momentum transfer concept was analyzed just using work/energy relationships subject to the conditions that the Lander could not experience an acceleration greater than 10g and that the Lander would initially be traveling at an orbital speed of 1.7 km/s. Because the constraint on the system is an acceleration and the frame of the moving Lander is not inertial, the system was analyzed using work/energy but in an inertial frame. This approach has obvious limitations; however, it also should provide a more conservative analysis meaning that, if the results are unfeasible for this simplified model, the addition of a gravitational component by the moon will only make exacerbate the outcome. Shown below is a plot of the acceleration felt by the Lander versus collision/spring distance through which some force must act to slow the Lander to zero. A reasonable distance for this “collision” would be between 1 and 2 meters since a spring of this relaxed length must be carried on the OTV with a mass less than that of the Lander descent propellant. From the graph, it can be seen that, at this distance, the accelerations are on the order of 1x105 Earth g’s. This is four orders of magnitude higher than that sustainable by the communications equipment (10g) and is probably higher than what is able to be withstood by the molecular bonds in the vehicular structure. Additionally, to maintain an acceleration less than 10g during a deceleration from 1.7 km/s it would be necessary to have a collision distance of approximately 150 km. For these reasons among others, the momentum transfer concept is infeasible. Momentum Transfer Alternative Acceleration sustainable by Communication Equipment: 10g Most Conservative Reasonable Collision Distance: 1-2 m Earth g’s Sustained at this Distance: 1x105 Collision distance required at 1.7 km/s = ~150 km Because the sustained acceleration in a reasonable spring collision would be four orders of magnitude higher than the communication equipment can withstand (and maybe higher than the molecular bonds of the structure can withstand) this alternative is entirely infeasible. Kris Ezra Attitude Group Translunar Phase

6. Rationale for Discarding Momentum Transfer Concept: The momentum transfer concept was analyzed just using work/energy relationships subject to the conditions that the Lander could not experience an acceleration greater than 10g and that the Lander would initially be traveling at an orbital speed of 1.7 km/s. Because the constraint on the system is an acceleration and the frame of the moving Lander is not inertial, the system was analyzed using work/energy but in an inertial frame. This approach has obvious limitations; however, it also should provide a more conservative analysis meaning that, if the results are unfeasible for this simplified model, the addition of a gravitational component by the moon will only make exacerbate the outcome. Shown below is a plot of the acceleration felt by the Lander versus collision/spring distance through which some force must act to slow the Lander to zero. A reasonable distance for this “collision” would be between 1 and 2 meters since a spring of this relaxed length must be carried on the OTV with a mass less than that of the Lander descent propellant. From the graph, it can be seen that, at this distance, the accelerations are on the order of 1x105 Earth g’s. This is four orders of magnitude higher than that sustainable by the communications equipment (10g) and is probably higher than what is able to be withstood by the molecular bonds in the vehicular structure. Additionally, to maintain an acceleration less than 10g during a deceleration from 1.7 km/s it would be necessary to have a collision distance of approximately 150 km. For these reasons among others, the momentum transfer concept is infeasible. Spinning Mass Tether Alternative Acceleration sustainable by Communication Equipment: 10g Required Tether Length to Match Orbital Velocity: ~50 km Additional mass cost at this Length: 325 kg (Total mass of 400 kg) Orbital Height: ~100 km Result: Weight of tether exceeds propellant mass and tether length is nearly half the orbital height. Completely infeasible. Kris Ezra Attitude Group Translunar Phase

7. Other Ideas • Calculation Slides which outline methodology alone • Slides which detail the actual setup of alternatives • For example, diagrams: Kris Ezra Attitude

8. References Valley Forge Composite technologies. “Sun Sensors,” Accessed 3 Feb 2009, URL: http://www.vlyf.com/aerospace/sun-sensors/ Kris Ezra Attitude